Electrical driving mechanism



June'ZO, 1950 c. T. HAYES 2,512,017

ELECTRICAL muvmc uscamsu Filed Sept. 25, 194.8

2 Sheets-Sheet 1 June 20, 1950 .Filed saw. 25, 1948 c. T. HAYES 2,512,017

ELECTRICAL DRIVING IIECHANISI 2 Sheets-Shoot 2 FIG-,2. I 3' r 15E LbWER 4 9* 31 39 as HA 7 l5 19 Ha M Ja Patented June 20, 1950 ELECTRICAL DRIVING MECHANISM Charles T. Hayes, Kenosha, Wis., assignor to Dynamatlc Corporation poration of Delaware Kenosha, Wis., a cor- Application September 25, 1948, Serial No. 51,240 In Great Britain September 30, 1947 8 Claims.

This invention relates to electrical driving mechanisms, and with regard to certain more specific features, to such mechanisms for cranes, hoists, winches and similar machinery.

Among the several objects of the invention may be noted the provision of electrical driving mechanisms for cranes, hoists, winches and similar machinery wherein the hoisting or lowering speed shall be infinitely variable between zero and a maximum; the provision of machinery of the class described which for a fixed setting of an operator-selective speed control, irrespective of the actual load being handled, effects a constant lifting or lowering speed of operation; the provision of apparatus of the class described which an A. C. motor. By the use of the combination herein, all the desirable features referred to, together with certain additional advantages, may be obtained in a. simple, inexpensive manner. The description refers primarily to the system as applied to a crane driven by an A. C. motor, but it will be apparent that the same system is applicable to any other machine requiring the same or similar characteristics and driven by the same or different type of electric motor.

The invention comprises a driving mechanism utilizing a constant-speed electric motor driving without overload on the equipment allows the selected speed to be achieved from rest in a minimum time period; and the provision of apparatus of the class described employing, if desired, an A. 0. motor as a prime mover. Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

Fig. 1 is a circuit diagram of the electrical parts; and,

Fig. 2 is an enlarged diagrammatic view primarily of the mechanica1 arrangements of the invention, including some circuit parts from Fig. 1.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

In the driving of cranes, hoists, winches and similar machinery, it is highly desirable that the speed of hoisting or lowerin shall be infinitely variable between zero and a maximum, and also that the particular speed selected by the operator shall remain constant for a fixed setting of the control, irrespective of the actual load handled. Moreover, it is equally desirable that the selected speed shall be achieved from rest in the minimum time period, consistent with the avoidance of overloads on any portion of the equipment. Previously it has not been possible to combine all these desirable features in any existing mechanism and in particular, difficulties have arisen in cases where the prime mover is 55 Med an eddy-current slip coupling or couplings controlling the crane or hoist, a solenoid-operated friction brake operatively interlinked with the coupling, an electronic excitation unit supplying D. C. to the field coil of the coupling and controlling the torque applied to the hoising drum and a controller for operating and for varying the hoisting and lowering speeds of the crane.

Referring now more particularly to the drawings, a motor I is direct-coupled to the input shaft 3 of an eddy-current slip coupling 5. This shaft is rotary in a suitable bearing 1 and drives a driving inductor drum 9 of said coupling 5. Thus the drum 9 is driven from the motor I. The driven field member of the coupling 5 is shown at II and carries a field coil l3. The drum 9 and field II are in electromagnetic drive relationship. The shaft 3 extends sufiiciently to support the member II and the parts connected therewith. These parts include a hollow output shaft assembly l5 rotary on said input shaft 3. The output shaft I5 is coupled to a hoisting drum ll of a crane, either directly or through a gear train l9 shown. A rotor 2| of a solenoidoperated friction brake 23 is also attached to the output shaft assembly I5. This brake is of the type having a brake band 25 which is automatically applied mechanically as by a spring when the solenoid indicated at 21 is deenergized.

The driven shaft 15 also carries the armature of an A. C. control generator 29, the stator of which is immovable. The shaft I5 also, through a chain drive 3|, drives the inductor drum 35 of the auxiliary eddy-current slip coupling 33. The driven field is indicated at 31. Field member 3! drives shaft assembly 15 through a gear train 34. The slip coupling 33 is supplied with current through commutator rings 39. The field coil [3 of the slip coupling 5 is supplied with current through commutator rings 41.

At 43 is shown a control potentiometer operby means of a lever 45. This lever controls a cam 46. Three switches 41, 48 and I95 are engaged by cam 46. Switches 41 and I95 are open only when the lever 45 is centrally positioned; otherwise these switches are closed. Switch 48 is open only when lever 45 is moved to a left or raise position. The central point corresponds to the neutral positions of parts wherein the mechanism is at rest. The two extreme positions correspond to hoisting at maximum speed or lowering at maximum speed, respectively. Intermediate lever positions correspond to intermediate hoisting or lowering speeds. The lever is preferably spring-loaded in its central position.

Referring now more particularly to Fig. 1, there is indicated at L-I, L-2 and L-3 a threephase A. C. power line connected to energize motor I through a line switch 49. One of these A. C. phases is connected by wires 5| and 53 to the primaries of three transformers 55, 51 and 59, and to two wires 6| and 63. Wires GI and 63 supply A. C. power to two rectifier tubes I35 and 61. Two condensers 68 and 10 are connected from the grid to thecathodes of power rectifier tubes 65 and 61, respectively. Tube 65 serves as a back rectifier for tube 61. A resistor 66 is shunted from'the anode to the grid of tube 65. The cathodes of tubes 65 and 61 are interconnected by wire 69, which is in turn connected to one side of the clutch coil I3 through a wire I I. The other side of clutch coil I3 is electricall connected through a wire 13 and a switch arm 300B to A. C. line 63. The anode of tube 61 is connected through a wire 64 and a switch arm 300A to A. C. line H.

The tubes 65 and 61, together with wires 6|, 63, 64, 69, H, 13, condensers 68, 10 and resistor 66 comprise an A. C. rectifier unit for feeding the clutch coil I3. The current drawn by'coil I3 is controlled by adjusting the grid bias of tube 61 as described below.

The grid of tube 61 is connected through a grid-blocking resistor 15 to a phase-shifting network 11. Network 11 includes the secondary of a transformer 19, a resistor BI and a condenser 83. The primary of transformer 19 is supplied with a single-phase A. C. power from the wires BI and 63 through two wires 85 and 81.

A wire 89 connects the phase-shifting network 11 through a double-throw solenoid-actuated switch arm I000 to either of two identical speedcontrol units 9I and 93. These control units are of the customary full-wave rectifier design comprising a transformer 95 having a centertapped secondary winding 91; a duo-diode tube 99; a filter condenser IN; and a bleeder resistor I03. When switch arm IO0C is in the depending ,on its positioning.

The primary windings of transformers 95 are parallel-connected through wires I 09 and III to the A. C. control generator 29, the potential output of the rectifier units 91 and 93 being dependent on the speed of generator 29.

The speed-controlled potential output of either rectifier unit 9I or 93 is connected in series with the D. C. potential output of a reference voltage rectifier unit II 3. This unit is of a customary full-wave rectifier design and includes a duodiode tube II1; a filter choke I I8; a filter condenser II 9, a resistor I29; a voltage regulator tube I2I; and a tapped bleeder resistor I23. The potentiometer 43 is connected across the regulated potential output of unit II3 b means of two wires I25 and I21, the former being of positive polarity, the latter of negative polarity. A resistor I29 is series-connected by means of wire I25 to a double-throw solenoid-actuated switch arm IO0D. Potentiometer 43 comprises two separate resistance sections, the left, or raise section, having a connection to the right contact of switch arm IIJIID through wire I33 and a connection to the right section of potentiometer 43; the other end of the right-hand section (lower) being connected through a wire I3I to the left contact of switch arm ND. The above description includes the broad principles specified in U. S. Patent 2,277,284 which amount to applying bucking voltages from a manually controlled network and from a coupling-drivenspeed control network to an energizing rectifying network feeding the coupling. However, the present above description includes the new idea of provision for reversing the polarity of the current supply from the coupling-driven-speed control network and from the reference voltage unit for selectively energizing the coupling, depending upon whether the coupling is to act as a clutch or a brake.

A torque-control unit adapted to produce a D. C. potentia1 which is a function of the load current of motor I is indicated generally at numeral I39. This unit I39 includes a current transformer winding I4I parallel-connected to a potentiometer I43; a transformer I45 having its primary connected across the rotor and one stator connection of potentiometer I43; a power tube I41; a screen grid connection 245; a grid resistor I5I; two condensers I53 and I55; a resistor I51; and a plate load resistor I59. The anode of tube I41 is connected to the cathodes of rectifier tubes 65 and 61 by means of a wire I6I when a double-throw switch arm I02 is in the right-hand position shown in Fig. 1. In the left position of switch arm I02, wire I6 I connects also through wire 204, which in turn is connected to wire I04, so that the anode circuit from tube I41 is completed to point 69. All switches IO0A, I02, I000 and IO0D operate mechanically at the same instant.

As will be seen below from the genera1 description, as the motor I overdraws a predetermined amount of current as determined by the setting of the potentiometer I43, the torque-control unit I39 fed by the current transformer I4I serves to vary the cathode-to-grid potential of tube 61. Since tube 61 in effect controls the excitation of the coil of coupling 5, this construction serves to prevent the motor load from exceeding a predetermined current value. In other words, if the motor I tends to draw current in excess of this predetermined amount, the coupling 5 will increase its slip. Thus the parts described in this paragraph include the broad principles shown in U." S. Patent 2,286,778, reissued as 22,432.

A triode relay actuator tube is indicated at numeral I 63. This tube and a shunt circuit, consisting of a relay coil I65, a condense I61 and a resistor I68, are series-connected across A. C. lines GI and 63 to form a low-voltage protective unit. The grid of tube I63 is connected through a resistor I69 having a condenser "I in shunt to a rotor arm of a potentiometer I13. This potentiometer I13 is series-connected with a resistor I15 across A. C. lines 8| and 83. A switch arm I11 of relay I85 is adapted to be energized by relay coil I85 only when the potential impressed upon the grid of tube I83 is sufilciently positive to cause tube I83 to conduct. Thus, switch arm I11 will remain closed only while the A. C. line voltage is above a predetermined value as set by positioning the arm of potentiometer I13. When the switch arm I11 is in the closed position shown in Fig. 1, an A. C. circuit from wires BI and 83 is completed through a relay coil 288 and solenoid-actuated switch arm 388A. This circuit will include wires I8I, I83 and I85. Relay coil 288 controls the operation of three singlethrow solenoid-actuated switch arms 288A, 2883 and 2880. Two wires I81 and I88 supply A. C. power to brake solenoid 21 when the switch arms 288A, 288B and 2880 are all in the closed position shown in Fig. 1, A. C. power being supplied to switch arms 2883 and 2880 through two wires I9I and I93. Only when switch arm 388A is closed can the A. C. circuit to the anode of tube 61 be completed through a wire 84. Also, only when switch arm 3883 is closed can the D. C. circuit to field coil I3 be completed through wire 13.

The A. C. control circuits of this device include also the switch I85. This switch is seriesconnected with switch 41 and a wire I81 from wire L-I to two switches I88 and 28I. These switches I89 and 28I may be manually operable, or, if desired, may be cam-operated by lever 45. Three wires 283, 285 and 281 interconnect these switches I99 and 28I with the double-throw solenoid-actuated switch arm 388A. A relay coil 388 is supplied with A. C. power through wire I91 and through a wire 288.

The cam 46 serves to actuate switch 48 as well as the switches 41 and I 35. Two relay coils indicated by numeral I88 are supplied with A. C. power through wires 2I3 and 2I5 from wires 5I and 53. These coils I88, when energized, serve to actuate switch arms I88A, I82, I880 and I88D to their left-hand or lower positions shown in Fig. 1. These switch arms remain in the righthand or raise position when coil I88 is not energized.

The transformer 59 supplies A. C. power to a bridge rectifier circuit 223. The rectified D. C. output of rectifier 228 is connnected by wires 23I and 233 to the field member 31 of the eddy-current slip coupling 33 through commutator rings 39. A rheostat 235 is connected across the bridge rectifier 229, the arm of this potentiometer being series-connected with wire 23I through a switch 231.

The filaments of the variouselectronic tubes described above are energized by means of transformer windings 2I1, 2I9, HI and 223. The electrical connections to these filaments have not been shown in the circuit diagram in the interest of clarity and brevity, but are connected in the customary manner.

Operation is as follows:

With control lever 45 in its neutral or central position, line switch 48 is closed and energy is supplied to the motor I, which rotates shaft 3 and inductor drum 9 at substantially constant rotational speed. The hollow output shaft I5 will remain stationary, being held in position by the friction brake 23 until the control lever 45 is moved from its central position. When arm 45 is centrally located, switches 41 and I are open, and switch 48 is closed. Tube I83 serves as a. half-wave rectifier and energizes relay coil I85 to move switch arm I11 to its closed position when alternating current of sufilcient potential is applied to wires 8I and 83.

To raise a load by means of hoisting drum I1, lever 45 must be moved to the left, thus closing switches 41 and I85 and opening switch 48. Switch arms I88A, I88C and I88D will then move to a right-hand position when relay coil I88 is deenergized by the opening of switch 48. In this position, switch arm I88A closes the circuit between wires 283 and 285. By moving switch I99 to a closed position, relay coil 388 will be energized through wires I81 and 288 to close switch arms 388A and 388B to the left. The A. C. circuit to relay coil 288 is thereby completed through switch arms I11 and 388A to A. C. lines 8| and 83.

The energization of relay coil 288 moves switch arms 288A, 2888 and 288C to the left, energizing the brake solenoid 21 through wires I9I, I81, I88 and I83 to release friction brake 23. Simultaneously with the closing of switch arms 388A and 3883, A. 0. power is available through wire 64 to the anode of tube 81 and D. C. power is available through wire 13 to complete the clutch rectifier circuit to energize the eddy-current coupling 5. The grid bias on tube 81 will determine the current flow through clutch coil I3 and thus the rate of hoisting. Initially the hoisting rate will be dependent only on the setting of lever 45 (which serves as the rotor of potentiometer 43) and the conduction of torque-control tube I41. The farther lever 45 is moved to the left, the more conductive will be tube 81. Thus, at any given setting of lever 45 the hoisting drum I1 will be rotated at a given desired and substantially constant rate. This rate of hoisting is reached in a minimum period of time consistent with no overload on motor I. The amount of torque delivered by motor I is determined by the setting of potentiometer I43. If the current through the current transformer exceeds this predetermined value, usually 100% of rated motor capacity, tube I41 will conduct, increasing the grid bias on tube 81 in a negative direction and thus decreasing the coupling through eddy-current, coupling 5. That is to say, the coupling 5 will slip more, permitting the motor to operate at or nearer its normal speed than it would if the coupling were not partially released.

When the rotational speed of drum I1 has reached the predetermined value as set by lever 45, any further increase in speed will increase the grid bias on tube 81 in a negative direction due to the action of speed-control unit 8|. The potential output of unit 9| is increased by an increase in the rotational speed of control generator 28. Thus, the rate of raising is determined by the composite grid bias made up of the potential selected from reference voltage unit II3 by potentiometer 43; the potential output of unit 8I and the potential output of the torque-control unit I39.

The grid bias supplied by unit 9|, unit I38 and unit II3 through potentiometer 43 has an A. C. rider wave component impressed upon it by phase-shifting network 11. This A. C. rider wave is of constant amplitude and is in a constant out-of-phase relationship with the A. C. anode voltage of tube 81.

The load carried by drum I1 may be brought to rest by returning the control lever 45 to the central position, whereby the friction brake 23 is automatically applied and the clutch coil I3 is deenergized. If it is desired to hold the load suspended for a lengthy period of time, the motor I may be deenergized or the line switch 49 may be opened. If at any time during operation there is a power failure, friction brake 23 is similarly applied automatically by the resulting deenergization of brake solenoid 21.

In order to lower a load, the control lever 45 is moved from the central position towards the right to a position corresponding to the desired speed of lowering. The first movement of lever 45 (when switch 20I is closed) closes switches 41, 48 and I95, simultaneously energizing the solenoid 21 to release friction brake 23 and energizing coupling 5. Relay coils I are energized through switch 48 to move switch arms lllIlA, I02, IDIlC and IUBD to the left. This action of switch arm IUBC connects the grid of tube 61 to speedcontrol unit 93 (thus disconnecting unit 9| from the circuit) and arranges the circuits so that an increase in speed of generator 29 increases rather than decreases the excitation of clutch coil I3. The actuation of switch arm IUIJD to the left disconnects the left section of potentiometer 43 and connects the right section. This action, it will be noted, reverses the polarity on potentiometer 43 so that at maximum lowering speed (lever 45 at maximum clockwise position), the wire I0! is connected to the negative side of reference voltage unit II3. At maximum raising speed (lever 45 at maximum counterclockwise position), the wire I0! is connected to the positive side of unit II3 through wires I33, I25 and resistor I29.

Upon this movement of lever 45 to the right, the load will commence to fall under the infiuence of gravity, the rate of lowering being dependent upon the positioning of lever 45. The eddy-current slip coupling 5 serves as an electromagnetic brake in the lowering of a load. The greater the energization of the clutch coil I3, the greater will be the braking effect upon the hoist drum II. As soon as the lowering speed attains a value corresponding to the position of lever 45, the eddy-current coupling 5 is excited by the action of the speed-control unit, increasing the conduction of tube 61 which brakes the load. At the same time, the desired-lowering speed is attained without exceeding the predetermined load value set by potentiometer I43 in the mimmum possible time period, under the influence of gravity, because the speed-control unit 93 does not cause the grid excitation of tube 61 to be modified sui'iiciently to excite the clutch coil I3 to exert a retarding influence until the desired speed is attained. The torque-control unit I39 thus functions as in hoist-raising; an increase over a predetermined load level decreasing the.

grid bias of tube Bl to increase the slip in coupling 5. Switch arm I02 is mechanically actuated to contact two common switch terminals through wires I04 and 244 so that torque-control impulses may function in either hoisting or lowering. Thus, the anode of tube I41 is connected properly in unison with switches IDEA, I000 and IOI'ID so as definitely to divide hoisting and lowering functions.

When the friction in the gear train I9 is such that the hook of hoisting drum II when unloaded will not fall under only the influence of gravity, or falls insufiiciently quickly, the auxiliary eddycurrent coupling 33 is arranged so as to drive drum I! in the reverse direction through gear train 34. This coupling 33 is energized only when the control lever 45 is moved to a lowering position. It is of a smaller size than coupling 5 inasmuch as it is only required to have a torque capacity adequate to overcome the friction in the mechanical system.

In the arrangement shown in the drawings, this auxiliary coupling 33 is only energized when lever 45 is moved to a position slightly beyond that corresponding to maximum lowering speed. At this extreme position, lever 45 closes switch 231 to energize clutch winding 31 through wires 23I and 233.

It is of course clear that the switch 231 could be operated from the lever 45 before the latter reaches the end of its action as a potentiometer control. In such event, the action of the second or auxiliary coupling 33 during lowering will be overcome by the eddy-current coupling 5 when the lowering speed selected by lever 45 is less than that attained only by the coupling 33. The speed of lowering due to coupling 33 is adjustable by rheostat 235.

In view of the-above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. Control apparatus for a hoist comprising a motor, an eddy-current slip coupling having'inductively coupled members and including a D. C. field coil, one of said members being connected to the motor and the other being connected to the hoist, an A. C. supply circuit, at least one rectifier tube fed by said A. C. circuit and supplying said field coil with direct current, a control grid in the tube, a second circuit including means for applying a predetermined constant biasing potential to said control grid, a generator connected with the hoist-connected coupling member having angular velocity in proportion thereto, a third circuit supplied from the generator and including means connected with said grid to apply a potential in coordination with said biasing potential to modify the bias on the control grid in accordance with said angular velocity, and a reversible manual control movable from a neutral position to a hoist-raising position or a hoist- -lowering position, said third circuit having components adapted to be selectively energized from said generator in accordance with the positioning of said manual control to cause more slip in the coupling in response to increasing speed of the hoist-connected coupling member in said hoistraising; position and less slip in the coupling in response to an increasing speed of the hoist-connected coupling member in said hoist-lowering position.

2. Control apparatus for a hoist comprising a motor, an eddy-current slip coupling having inductively coupled members and including a D. C. field coil, one of said members being connected to the'motor and the other being connected to the hoist, an A. C. supply circuit, at least one rectifier tube fed by said A. C. circuit and supplying said field coil with direct current, a control grid in the tube, a second circuit including means for applying a predetermined constant biasing potential to said control grid, a generator connected with the hoist-connected coupling member having angular velocity in proportion thereto, a third circuit supplied from the generator and connected with said grid to apply a potential in coordination with said biasing potential to modify the bias on the control grid in accordance with said angular velocity, a reversible manual control movable from a neutral position to a hoist-lowering position or a hoistraising position, said third circuit having components adapted to be selectively energized from said generator in accordance with the positioning of said manual control to cause either more or less slip in the coupling in response to an increasing speed of the hoist-connected coupling member, and a torque-control unit responsive to current supplied to said motor adapted to apply additional control voltage to the grid of said tube to vary the slip of said coupling in accordance with current drawn by the motor.

3. Control apparatus for an eddy-current slip coupling having inductively coupled members and including a D. C. field coil, comprising a motor driving one of said members, an A. C. supply circuit, at least one rectifier tube fed by said A. C. circuit and supplying said field coil with direct current, a control grid in the tube, a reference voltage unit for applying a predetermined constant biasing potential to said control grid, a speed-control unit energized by the other coupling member adapted to produce a potential which is a, function of the angular velocity of such member, said speed-control unit being connected to said grid to apply a potential in coordination with said biasing potential to modify the bias on the control grid in accordance with said angular velocity, a reversible manual control movable from a neutral position to a hoist-raising position or a hoist-lowering position, switch com ponents adapted to be selectively energized from said speed-control unit in accordance with the positioning of said manual control to cause either more or less slip in the coupling in response to an increasing speed of the hoist-connected coupling member, a brake on said other coupling member, and switching means actuated by said manual control for setting said brake when th control is in said neutral position.

4. Control apparatus for a hoist comprising a motor, an eddy-current slip coupling having inductively coupled members and including a D. C. field coil, one of said members being connected to the motor and the other being connected to the hoist, an A. C. supply circuit, at least one rectifier tube fed by said A. C. circuit and supplying said field coil with direct current, a control grid in the tube, a second circuit including means for applying a predetermined constant biasing potential to said control grid, a generator connected with the hoist-connected coupling member for angular velocity proportional thereto, a third circuit supplied from the generator and including means connected with the grid to apply a, potential in coordination with said biasing potential to modify the bias on the control grid in accordance with said angular velocity, said third circuit having components adapted to be selectively energized from said generator respectively to cause either more or less slip in the coupling in response to speed increase of the hoist-connected coupling member, a reversibly movable manual control means for effecting selection of said components according to whether the hoist is to be raised or lowered, a brake on the hoist-connected coupling member, and apparatus for setting said brake from the manual control means when the latter is in a, neutral position between its hoist-raising and hoist-lowering positions or upon failure of said A. C. supply circu1 5. Control apparatus for a hoist comprising a motor, an eddy-current slip coupling having inductively coupled members and including a DC. field coil, one of said members being connected to the motor and the other being connected with the hoist, an A. C. supply circuit, at least one rectifier tube fed by said A. C. circuit and supplying said field coil with direct current, a control grid in the tube, a second circuit including means for applying a predetermined constant biasing potential to said control grid, a speedcontrol unit energized by said hoist-connected coupling member adapted to produce a potential which is a function of the angular velocity of said last-said member, said speed-control unit being connected to said grid to apply potential in coordination with said biasing potential to modify the bias on the control grid in accordance with said angular velocity, a. reversible manual control movable from a, neutral position to a, hoist-raising position or a'hoist-lowering position, switch components adapted to be selectively energized from said generator in accordance with the positioning of said manual control to cause either more or less slip in the coupling in response to an increasing speed of the hoist-connected coupling member, depending upon whether the hoist is to be raised or lowered, a second eddy-current coupling operatively connecting the motor with the hoist adapted when energized to overcome friction in the hoist connection to allow the hoist to drop, and apparatus responsive to positioning of said manual control to a lowering position to energize said second coupling.

6. A hoist control comprising an eddy-current slip coupling having one member connected to an electric motor and a second member connected to a shaft, a D. C. field coil carried by one shaft to produce a first potential which is a function of the rotational speed of said shaft, a reference voltage unit adapted to produce a second potential, 3, potentiometer shunt-connected with said reference voltage unit, a torque-control unitadapted to produce a third potential which is a function of the load current of said motor, a clutch rectifier unit having at least one rectifier tube including a grid and a cathode adapted variably to energize said field coil, and switch components movable between a first position wherein an increasing angular velocity of said shaft varies said first potential to decrease said field coil energization and a second position wherein an increasing angular velocity of said shaft varies said first potential to increase said field coil energization; said speed-control unit, said reference voltage unit and said torque-control unit being series-connected between said grid and said cathode, said potentiometer being adjustable to vary the grid bias on said rectifier tube, said rectifier tube being responsive to the composite potential of said speed-control unit, said torque-control unit and said potentiometer to energize said field coil.

7. A hoist control comprising an eddy-current slip coupling having one member connected to an electric motor and a second member connected to a shaft, a D. C. field coil carried by one of said members, an electrically actuated brake for said shaft, a hoisting drum connected to said 11 shaft, a speed-control unit adapted to produce a potential which is a function of the rotational speed of said shaft, a reference voltage unit adapted to produce a D. C. potential, a potentiometer shunt-connected with said reference voltage unit, a manually operable arm afilxed to said potentiometer movable from a neutral position to a hoist-raising or hoist-lowering position,

a switch actuated by said. arm electrically to release said brake and permit energization of said field coil in said raising or lowering positions, a torque-control'unit energized by current to said motor adapted to produce a potential which is a function of the load current of said motor, and a rectifier unit having at least one rectifier tube including a grid and a cathode adapted variably to energize said field coil; said speed-control unit, said reference voltage unit and said torque-eontrol unit being series-connected between said grid and said cathode, said rectifier tube being responsive to the composite potential of said speedcontrol unit, said torque-control unit and said potentiometer being adapted to energize said field coil to prevent the rotation of the hoisting drum above a predetermined speed dependent on the adjustment of said potentiometer and to prevent the load current of said motor from exceeding a predetermined value.

8. Control apparatus for an eddy-current slip coupling having inductively coupled members and including a D. C. field coil, comprising a motor 12 driving one of said members, an A. C. supply circuit, at least one rectifier tube fed by said A. C. circuit and supplying said field coil with direct current, a control grid in the tube, a reference voltage unit for applying a predetermined constant biasing potential to said control grid, 2. speed-control unit energized by the other coupling member adapted to produce a potential which is a function of the angular velocity of such member, said speed-control unit being connected to said grid to apply a potential in coordination with said biasing potential to modify the bias on the control grid in accordance with said angular velocity, and switch components movable between a first position wherein an increasing angular velocity of said other member varies said speedcontrol unit potential to decrease said field coil current and a second position wherein an increasing angular velocity of said other member varies said speed-control unit potential to increase said field coil current.

CHARLES T. HAYES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,277,284 Winther Mar. 24, 1942 2,286,778 Winther June 16, 1942 

